Thrower wheel of a mechanical stoker

ABSTRACT

A thrower wheel of a mechanical stoker is provided. The thrower wheel includes a plurality of blades, which are disposed on a base plate. A height of the blades increases in a radial direction in at least one area and optionally remains the same in one or more remaining areas, and the height of the blades is less at the inner end of the blades than at the outer end of the blades.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Stage of International Application No. PCT/EP2009/051619 filed Feb. 12, 2009, and claims the benefit thereof. The International Application claims the benefits of German Application No. 10 2008 009 683.0 DE filed Feb. 18, 2008. All of the applications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to a thrower wheel of a spreader stoker having a plurality of blades disposed on a base plate as well as to a corresponding spreader stoker.

BACKGROUND OF INVENTION

The invention can be used in firing plants having thrower wheel mechanical stoking. In said applications the solid, particulate fuel is introduced into the combustion chamber with the aid of the thrower wheel disposed in a spreader stoker. The trajectory length can be adjusted by varying the rotational speed of the thrower wheel.

Generally the thrower wheel is in this case arranged horizontally, in other words the axis of rotation of the thrower wheel is oriented vertically. The fuel is introduced from above in the region of the hub of the thrower wheel into the housing of the spreader stoker and then conveyed with the aid of the blades of the thrower wheel horizontally outward and—through openings in the spreader stoker—into the combustion chamber.

In the prior art thrower wheels in which the blades have a constant height were used for this purpose.

Depending on the type of fuel, however, the thrower wheel rotating at high speed is subjected to a high rate of wear. Upon entering the spreader stoker the fuel particles impinge only on the top edge of the blades and therefore are accelerated only impulsively to the requisite exit velocity. This results in high losses during transfer of the kinetic energy of the thrower wheel onto the fuel, which transfer is associated with a high rate of wear of the blades of the thrower wheel.

One possible way of reducing the rate of wear would now consist in adjusting the rotational speed of the thrower wheel to as low a setting as possible. However, this means that the trajectory length for the fuel is limited and possibly the optimal fuel distribution in the combustion chamber will not be reached.

SUMMARY OF INVENTION

An object of the invention is to improve the energy transfer from the thrower wheel onto the fuel and thereby reduce the wear on the top edges of the blades of the thrower wheel.

The object is achieved by a thrower wheel as claimed in the independent claim, according to which the height of the blades increases in the radial direction at least in one section and where appropriate remains the same in one or more other sections, and the height of the blade at the inner end of the blade is less than at the outer end of the blade.

In other words, the height of the blade therefore increases toward the outside, though it can also remain the same over some sections, but must not decrease in any section. In any event the blade is less high on the inside than on the outside. As a result, as the fuel particles travel outward, they impinge on higher and higher blade sections, in the process sliding along the blades toward the outside, and are accelerated continuously without impulses.

As a consequence thereof, the wear load is distributed from the inner top edge of the blade over a greater surface area, thereby reducing the wear on the top edge of the blade.

Since in addition a better transfer of kinetic energy from the thrower wheel onto the fuel is achieved as a result of the reduction in the impulses, the rotational speed of the thrower wheel can be reduced.

A possible embodiment variant consists in the height of the blades being increased from the inner end on in a first section and subsequently remaining the same in a second section as far as the outer end. This has the advantage that in the inner section of the blades, where normally the fuel is supplied, the fuel is accelerated continuously at the ascending top edges of the blades and in the second section, where no more fuel is directly supplied from above, it continues to be guided toward the outside.

In the ideal case the height of the blade at the inner end should be equal to zero. If this means that the rigidity of the blade is not guaranteed, the blade can be strengthened further outward, for example by means of additional metal plates.

The inventive effect should, however, also be established in any event if the height of the blades at the inner end is less than half the maximum height of the blades.

Needless to say, the effect of the invention can be increased if the blades are moved away from the region of the hub of the base plate, since the fuel is, of course, usually supplied concentrically to the hub. In this regard it can be provided that the inner ends of the blades have a clearance relative to the hub of the base plate.

Apart from the height of the blades, the arrangement and shape of the blades can be varied according to requirements: the blades can be straight or curved; they can run radially outward from the hub, they can be arranged tangentially relative to the hub or they can touch the hub neither directly nor indirectly (via an imaginary extension). The blades can directly adjoin the hub or indeed start only at a distance from the hub.

Usually, however, the blades will always extend as far as the rim of the base plate and are fixedly joined to the base plate along the entire length of the bottom edge.

The number of blades also depends on the type of fuel and fuel quantity. Two, four or six blades are common.

If the inventive thrower wheel is installed in a spreader stoker, then the latter comprises at least one housing having at least one feed opening for fuel and at least one ejection opening for fuel.

In this case a feed opening for fuel is indeed beneficially provided which is concentric to the axis of rotation of the thrower wheel, such that fuel can be applied onto the thrower wheel in the direction of the axis of rotation.

Equally a circumferential ejection opening for fuel can be provided which is arranged normal to the axis of rotation of the thrower wheel such that fuel in the plane of the thrower wheel can be ejected out of the thrower wheel.

In order to ensure that the fuel impinges in that section where the blade height is low it can be provided that the maximum height of the blades is attained only outside of the diameter of the feed opening.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the invention is shown in the figures and is explained below.

FIG. 1 shows a schematic view of a spreader stoker having a thrower wheel according to the existing prior art (on the left) and according to the invention (on the right),

FIG. 2 shows a view and plan view of an inventive thrower wheel having straight blades,

FIG. 3 shows a view and plan view of an inventive thrower wheel having curved blades.

DETAILED DESCRIPTION OF INVENTION

FIG. 1 is a schematic representation of a spreader stoker in the housing 1 of which a thrower wheel is disposed. The housing 1 has a central feed opening 5 through which fuel (see arrows) can be supplied from above.

Said fuel (see arrows) exits from the housing 1 again through the ejection opening 6.

In this arrangement the fuel is conveyed by means of the thrower wheel. This consists of a base plate 2, a hub 8 and blades. The left part of the figure shows a thrower wheel having conventional blades 4 which have a constant height over their entire length.

The right part of the figure shows a thrower wheel according to the invention having blades 7 whose height increases from the inside to the outside. In a first section the height of the blade 7 increases from a height that is less than half the maximum height of the blade, up to the maximum height. In the second section the height of the blade 7 stays the same up to the outer end of the blade 7 (maximum height). In this case the hub 8 is the same height as the inner end of the blade 7. The first section of the blade, which directly adjoins the hub 8, extends approximately up to halfway along the blade. The important thing, however, is the ratio to the feed opening 5, whose diameter—viewed in the radial direction—ends before the blade 7 has reached its maximum height.

What is achieved by feeding the fuel from above is that the fuel particles fall as far as possible below the top edge of the blades or, as the case may be, even as far as the base plate. Consequently the fuel particles are not just conveyed by the top edge of the blade but are swept up by the entire blade, which is lower in this section, and conveyed toward the outside.

FIG. 2 shows another possible embodiment of the thrower wheel. In this case four blades 7 are mounted on the base plate 2. The blades 7 do not adjoin the hub 8 on their inside, but are offset outward by approximately a third of the radius of the base plate 2. The inner height of the blades is chosen as low as possible, approximately corresponding to the thickness of the metal plate of the blades. The height of the blades increases along a straight line and the maximum height is reached after approximately ⅔ of the length of the blade 7.

FIG. 3 shows a further embodiment variant of the thrower wheel. Here, too, four blades 7 are disposed on the base plate 2, although in this case the blades 7 are curved and tangentially abut the hub 8. At their inner end the blades 7 have a height of somewhat less than half the maximum height. The maximum height of the blades 7 is reached roughly after half of the length of the blades.

Highly wear-resistant steel is used as a material for the blades.

The base plate 2 of the thrower wheels shown here has a diameter of 450 mm, while the maximum height of the blades 7 equals 85 mm. These dimensions will always need to be adjusted to suit a specific installation, however. 

1.-9. (canceled)
 10. A thrower wheel of a spreader stoker, comprising: a base plate with a hub; and a plurality of blades disposed on the base plate, wherein a height of the blades increases in a radial direction at least in one section, and wherein the height of the blades at the inner end of the blades is less than at the outer end of the blades.
 11. The thrower wheel as claimed in claim 10, wherein the height remains unchanged in one or more sections of the blades.
 12. The thrower wheel as claimed in claim 10, wherein the height of the blades increases from the inner end on in a first section and subsequently remains the same in a second section as far as the outer end.
 13. The thrower wheel as claimed in claim 10, wherein the height of the blades at the inner end is equal to zero.
 14. The thrower wheel as claimed in claim 10, wherein the height of the blades at the inner end is less than half the maximum height of the blades.
 15. The thrower wheel as claimed in claim 10, wherein the inner ends of the blades have a clearance relative to the hub of the base plate.
 16. A spreader stoker, comprising: a housing with a feed opening for fuel; an ejection opening for fuel; and a thrower wheel, the thrower wheel comprising: a base plate with a hub; and a plurality of blades disposed on the base plate, wherein a height of the blades increases in a radial direction at least in one section, and wherein the height of the blades at the inner end of the blades is less than at the outer end of the blades.
 17. The spreader stoker as claimed in claim 16, wherein the feed opening for fuel is concentric to an axis of rotation of the thrower wheel such that fuel is applied onto the thrower wheel in a direction of the axis of rotation.
 18. The spreader stoker as claimed in claim 16, wherein the ejection opening is a circumferential ejection opening being disposed normal to an axis of rotation of the thrower wheel such that fuel in a plane of the thrower wheel is ejected from the thrower wheel.
 19. The spreader stoker as claimed in claim 17, wherein the ejection opening is a circumferential ejection opening being disposed normal to an axis of rotation of the thrower wheel such that fuel in a plane of the thrower wheel is ejected from the thrower wheel.
 20. The spreader stoker as claimed in claim 16, wherein a maximum height of the blades is reached only outside of a diameter of the feed opening.
 21. The spreader stoker as claimed in claim 17, wherein a maximum height of the blades is reached only outside of a diameter of the feed opening.
 22. The spreader stoker as claimed in claim 18, wherein a maximum height of the blades is reached only outside of a diameter of the feed opening.
 23. The spreader stoker as claimed in claim 16, wherein the height of the blades remains unchanged in one or more sections of the blades.
 24. The spreader stoker as claimed in claim 16, wherein the height of the blades increases from the inner end on in a first section and subsequently remains the same in a second section as far as the outer end.
 25. The spreader stoker as claimed in claim 16, wherein the height of the blades at the inner end is equal to zero.
 26. The spreader stoker as claimed in claim 16, wherein the height of the blades at the inner end is less than half the maximum height of the blades.
 27. The spreader stoker as claimed in claim 16, wherein the inner ends of the blades have a clearance relative to the hub of the base plate. 